Ultra-fine metallic particles and flakes (e.g. copper particles and flakes) have many unique physical and chemical characteristics, which make them ideal materials for a variety of applications, such as electronics, catalysis, metallurgy, and decorative. The techniques of flattening metallic particles to produce flakes is well-known in the art. However, while the protocols for processing precious metals (e.g. silver and gold) are relatively simple, the milling of metallic particles, such as ultra-fine copper particles, in an open system (i.e. with exposure to air), is a very challenging task because the particles and flakes are readily oxidized in the air. In the case of copper, the milling of copper particles to flakes was routinely performed either by excluding the oxygen from the system (i.e. using a closed system) or in the presence of agents which dissolve the copper oxides formed during milling. These procedures, however, are expensive and difficult to implement and may lead to significantly lower yields of copper flakes and require expensive waste treatment. The present invention provides an environmentally friendly, low cost milling process which generates copper flakes with an superior dispersibility in non-aqueous solvents (e.g., low and medium polarity organic solvents) and oxidation resistance.